Soldering flux with improved shelf life



, 182K408 Patented Mar. 18, 1958 SGLDERING FLUX wrrn nvirnovnn SHELF LIFE Meyer 1.. Freedman, leveland, Ohio, assignor to Horizons Incorporated, Princeton, N. 3., a corporation of New Hersey No Drawing. Application April 15, 1955 Serial No. fi1,729

9 (Ilairns. (Cl. 148-23) This invention relates to a composition useful in joining aluminum and its alloys and includes the use of the composition as a means for joining the metals as well as the application of the composition in conjunction with a solder.

The joining of aluminum and aluminum alloys, that is alloys containing substantial percentages of aluminum, is generally rendered difiicult by the presence of a natural oxide film which forms on the surface of the metal whenever the metal surface is exposed to the atmosphere.

Processes previously suggested for the joining of aluminum or aluminum alloy articles include the use of many compositions based on one or more chlorides of metals which react with aluminum to deposit the metal by a simple displacement reaction and particularly one or more heavy metal chlorides of the group including zinc, tin, lead and cadmium chlorides either alone or in combination with one another or in combination with additional ingredients which attack the tenacious refractory film of naturally occurring aluminum oxide. Other prior art proposals for joining aluminum involve the mechanical removal of the naturally occurring oxide after the application of heat and a joining metal or alloy such as a solder.

I have now discovered a heavy metal chloride composition prepared in accordance with my invention which is free from the disadvantages inherent in prior art compositions.

lt is one object of this invention to provide a composition which has a shelf like considerably greater than that of prior art reaction flux compositions.

It is another object of this invention to provide a reaction flux composition which may be employed for joining two or more pieces of aluminum or aluminum alloys when used alone or in combination with a solder.

These and other objects will become readily apparent to those skilled in the art from the following specification and claims.

In accordance with my invention there is first prepared a mixture including one or more chlorides of metals more electropositive than aluminum such as zinc chloride, tin chloride, lead chloride and cadmium chloride. To this mixture there may be'added minor amounts of one or more chlorides of the alkali metals or ammonium chloride and there may also be added organic chlorides Whose ability to flux the oxide film is well known such as betaine chloride, hydrazine chloride, or other amine chlorides and other organic chlorides which do not produce large amount of carbon residue at the temperature of application. Furthermore, these compositions may also include a finely divided metal solder.

The solid constituents of my reaction flux composition may be either mixed dry or pre-melted before grinding to produce a material having a melting point considerably lower than the melting point of the mixture alone. The solid ingredients may be dry ground separately and then mixed together before incorporation of the anti-hygroscopic agents, or the entire composition may be wet ground at one time.

When the ingredients have been mixed together it has been observed that compositions not containing any antihygroscopic agent rapidly take up moisture from the atmosphere and that within a relatively short interval of time, a mixture which was entirely satisfactory at the time of its preparation has been rendered much less satisfactory, and indeed in many instances may have been rendered completely unsatisfactory for the purpose intended. In many instances, the amount of moisture absorbed in as short an interval as 30 minutes is sufficient to prevent the flux composition from functioning satisfactorily.

I have found that by coating the flux particles with an agent which is chemically inert with respect to such particles, which is not a solvent for the fiux particles, which is not volatile at room temperature and which will volatilize almost completely at 660 F., the harmful hygroscopic effect, above noted, can be prevented. While many organic compounds are sufiiciently volatile for the intended purpose, their use is hazardous because, under the soldering conditions, they are inflammable. Certain relatively uninfiammable chlorinated hydrocarbons have been found to produce the desired result. Among those which are sufficiently volatile at elevated temperatures and which produce a minimum of undesirable residue in use are the chlorocthylenes, particularly perchloroethylene. In usin this material it has been found necessary merely to submerge the powdered prior art hygroscopic reaction flux in the perchloroethylene. Amounts between about 10% and 30% by weight of the flux ingredients are effective with between and being preferable.

The effectiveness of compositions containing up to about 30% of perchloroethylene was demonstrated by preparing duplicate compositions, exposing them to the air for various periods and then attempting to join strips of type 23 aluminum alloy together, as set forth in the following example.

Example I A mixture of grams ZnCl 14 grams SnCl and 10 grams of NaCl was ground to fine powder and divided into two portions, A and B. Portion B was then made into a paste by mixing with 15 grams of perchloroethylene and 0.1 grams of a silicone oil having a viscosity of 1000 centistokes at 77 F. Both portions were tested and found to work equally well when freshly prepared. The test consisted of placing a /2 gram portion of flux upon a horizontal plate of 28 aluminum. A 3" long strip of 28 aluminum, 0.02" thick and 1" high was supported vertically upon the horizontal plate. The center portion of the vertical strip contacted the flux. The horizontal plate was then heated from below to 700 F. by a gas flame, causing the flux to react with the aluminum and form a molten alloy which joined the two pieces of aluminum together.

After 4 hours of exposure to normal atmospheric conditions, flux portion A had become damp and caked. It was tested at this time and found to give only a partial bond, and to leave considerable unreacted residue. Portion B in which the flux particles were coated with the perchloroethylene, was not aifected by 4 hours exposure and produced a reaction bond similar to the bond produced when the composition was freshly prepared. After 20 hours exposure, flux portion A had become" wet and pasty. A successful reaction bond could not be made with the wet material. 0n the other hand, flux B after 20 hours still produced a good joint.

The effectiveness of my anti-hygroscopic addition is further enhanced by the addition of other relatively volatile materials which tend to slow down moisture pick-up and specifically by the addition of a liquid polyalkylsiloxane, such as methylsilicone oil or ethylsilicone oil, either of which may be added to the composition in an amount of up to 10%, and preferably between about 2% and 10% by weight, without producing'carbon residue or other. in-

terference with the joining operation. The following exple l u t t s. such a omposit n,

7 7 Exa p e l! 7 mixture was formed from the following chlorides in finely powdered condition: rams s a n us hlo d 20 g am cadm um ch r 2. lead chloride 7 8 stem ammo i m h ride 12 carbon atoms in the chain. "Ihes'e' agents decompose at the temperature of reaction bonding, although the residue has been found not to interfere with the joining process. flux composition directly or in the form of their salts with mineral acidsor organic acids of low molecular weight. Because ofnthe carbonaceous residue,'it is preferredto limit the amount of such amines of amine salts to less'than 2% by weight of the total composition. The following example. illustrates a composition including such a primary amine salt.

Exam le 11 The following ingredients were placed in a porcelain ball mill and ground to a fine paste:

34 grams zinc chloride 20 grams stannous chloride 9 grams sodium chloride 20 grams perchloroethylene 0.2 gram s'tearylamine acetate The paste performed very satisfactorily at a temperature of 650 F. and produced a joint having a heavy fillet at 700 F. with types 2 S, 38 and 61S aluminum alloys. It was alsolused satisfactorily as a flux for various solders.

Other chloroethylenes may be employed; A composition containing trichloroethylene is shown below.

Eztwm e IV Finely powdered inc chloride, sodium chloride and ammonium chloride were mixed with trichloroethylene and a silicone oil in the following proportions:

74 ams l cchlo id 2 grams sed um chlo ide 11 grams ammonium chloride .33 gr ms trichlo etbylen ,1 g ams si cone oil (100. cen stokes viscosity) The n-al'kyl primary amines may be added to the the eliectiveness of the polyalkylsiloxane as an anti-hy groscopic agent is sufficient that it may be employed without a chloroethylene.

I claim:

1. A soldering flux consisting essentially of particles of at least one chloride of a metal which is electropositive with respect to aluminum and a minor amount of particles ofat least one chloride from the group consisting of the alkali metal chlorides and ammonium chloride, said flux particles being coated with at least one andhygroscopic. agent in which said flux particles are insoluble and which is chemically inert with respect "to said particlesQsaid anti-hygroscopic agent being nonvolatile at room temperature, almost completely volatile at 600 F. and not leaving any deposits on volatilization which are detrimental in the soldering of metal.

2. A soldering flux asset forth in claim 1 in which said anti-hygroscopic agent is a compound selected from the group consisting of chloroethylenes and polysiloxanes.

3. A soldering 'fiux as set forthin claim 1 in which said anti-hygroscopic agent contains asan essential constituent from about 2% to l0%, by weight, of a polysiloxane from the group consisting of polymethyl siloxane and polyethylsiloxane.

4- .A ld ring flux as set forth in claim 1 in wh h said anti-hygroscopic agent contains as an essential constituent from about 10% to 30%, by weight, of a chloroethylene from the group consisting of trichloroethylene and perchloroethylene.

5. A soldering flux as set forth in claim 1 in which at least one chloroethylene andat least one polysiloxane are present as anti-hygroscopic agents.

6. A soldering flux as set forthin claim 1 in which the metal which is electropositive with respect to aluminum is one from the group consisting of zinc, tin, lead and cadmium.

7. The method of improving the shelf life of particles of a soldering flux containing heavy metal chloride particles, which comprises preparing the flux and thereafter coating the flux particles with at least one anti-hygroscopic agent in which said flux particles are insoluble and which is chemically inert with respect to said particles, said anti-hygroscopic agent being non-volatile at room temperature, almost completely volatile at 600 F. and not leaving any deposits onvolatilization which are detrimental in the soldering of'metal. v

8. The method of improving the shelf life of particles of a soldering flux as set forth in claim 7 in which said anti hygroscopic agent is a compound selected from the group consisting of chloroethylenes and polysiloxanes. 9. The method of improving the shelf life of particles of a soldering flux as set forth in claim 7 in which the anti-hygroscopic coating agent consists essentially of at least one chloroethylene and at least one polysiloxane.

ferences Cited inth file of this patent UNITED STATES PATENTS 2,238,068 Miller Apr. 15, 1941 2,325,014 Prendergast July 20, 1943 2,493,372 Williams Jan. 3, 1950 2,548,690 Vieno, Apr. 10, 1951 OTHER REFERENCES Silicones and Their Uses, R. R. McGregor, pages 49-51, 1954. (Copy'in Div. 50.) 

1. A SOLDERING FLUX CONSISTING ESSENTIALLY OF PARTICLES OF AT LEAST ONE CHLORIDE OF A METAL WHICH IS ELECTROPOSITIVE WITH RESPECT TO ALUMINUM AND A MINOR AMOUNT OF PARTICLES OF AT LEAST ONE CHLORIDE FROM THE GROUP CONSISTING OF THE ALKALI METAL CHLORIDES AND AMMONIUM CHLORIDE, SAID FLUX PARTICLES BEING COATED WITH AT LEAST ONE ANTIHYDGROSCOPIC AGENT IN WHICH SAID FLUX PARTICLES ARE INSOLUBLE AND WHICH IS CHEMICALLY INERT WITH RESPECT TO SAID PARTICLES, SAID ANTI-HYGROSCOPIC AGENT BEING NONVOLATILE AT ROOM TEMPERATURE, ALMOST COMPLETELY VOLATILE AT 600*F. AND NOT LEAVING ANY DEPOSITS ON VOLATILIZATION WHICH ARE DETRIMENTAL IN THE SOLDERING OF METAL. 